Laserfiche WebLink
5.0 OVERBURDEN STABILITY <br />Stress conditions in the overburden before and after excavation of the mains are <br />compared using FLAC31) (Fast Lagrangian Analysis of Continua). FLAC is a finite- <br />difference code suitable for geotechnical analyses of multilayered geologic material. <br />Because it can include multiple material properties for different horizons, it has been <br />widely applied in modeling coal mine stratigraphy. <br />Details of these analyses are presented in attachment A, including an examination of <br />different stresses in the overburden under typical cover of 500-ft. Figure 1 presents a <br />detailed view of model area, and figure 17 is the generalized stratigraphy used in these <br />analyses. Lines of symmetry are employed on model boundaries, and thus the area shown <br />is only a fraction of total modeled area. The models are entirely elastic with load transfer <br />to panel boundaries simulated through beams. <br />Mining geometry consists of a five-entry development system with 18-ft spans. <br />Modeling is simulated in two steps, including geologic consolidation (premining stress <br />state), and development of the mains. By comparing stress conditions prior to and after <br />development, the influence of mining on overburden stability is clearly visualized. The <br />model is loaded in the X and Y direction with expected horizontal stress field that <br />accounts for topographic conditions (section 3.2). The worst case condition is evaluated <br />by orienting the horizontal stress parallel to the rooms and crosscuts; <br />Sxx= Maximum applied horizontal stress= 1520 psi <br />Syy= Minimum applied horizontal stress= 420 psi <br />0 <br />Maleki Technologies, Inc. Page 31